There are several conventional approaches to forming a connection between a circuit board component (e.g., a connector, an integrated circuit or IC, etc.) and a circuit board. One approach, which is called the compression-fit or press-fit approach, involves the mating of specialized compression-fit pins of the circuit board component with circuit board vias (i.e., metal plated-through holes in the circuit board). One type of compression-fit pin (referred to as an eye-of-the-needle press-fit pin) is a metallic shaft having a hole or channel cut through the shaft in order to separate at least a portion of the shaft into two approximately parallel extending members. The total cross-sectional diameter of the shaft (i.e., the two extending members and the hole) of this compression-fit pin is slightly larger than the cavity of its corresponding via. Accordingly, when the compression-fit pin inserts within the via, metal sides of the via compress (i.e., squeeze) the two extending members of the compression-fit pin shaft toward each other. The frictional forces between the via and the shaft hold the pin in place and provide suitable electrical contact for carrying electrical signals between the pin of the circuit board component and the via of the circuit board.
Another type of compression-fit pin (referred to as a turret press-fit pin) has V-shaped notches cut along the side of a segment of the pin. Here, the total cross-sectional diameter of the segment is slightly larger than the via cavity such that, when the compression-fit pin inserts within the via, the edges of the notched segment cut into the metallic sides of the via (with metallic debris collecting in the notches of the pin) in order to form suitable electrical contact.
Some compression-fit pins have extending detention portions that laterally extend from the pins to prevent the pins from inserting too deeply within the vias. That is, when the pins insert into the vias, the pins continue to pass into the via cavities until the detention portions contact the tops of the vias (and perhaps the circuit board surface depending on the size of the detention portions). At this point, the detention portions provide an interference fit against the via tops preventing the pins from inserting further into the via cavities in order to provide the proper insertion depth for the pins within the circuit board vias.
Another approach to forming a connection between a circuit board component and a circuit board is to form a solder joint between pins of the circuit board component and vias of the circuit board. In contrast to the compression-fit pin which has a hole or channel through the shaft in order to form two approximately parallel extending members, a typical soldering pin has a substantially symmetrical and uniform cross-section (e.g., a circular cross-section or a square cross-section) which is typically half the size of the inner diameter of the corresponding vias of the circuit board in order to enable solder to easily flow within the via cavities between the pins and the inner surfaces of the vias to form solder joints. For example, for a soldering pin having a diameter of 0.018 inches (xe2x80x9c18 milsxe2x80x9d), the diameter of the via cavity is typically 0.039 inches (xe2x80x9c39 milsxe2x80x9d).
One soldering approach involves a process called wave-soldering. In this approach, pins of the component insert through vias of the circuit board such that the component rests in its intended mounting location. Then, the circuit board passes over a wave of melted solder, i.e., solder heated until it is in liquid form (e.g., 500 degrees Fahrenheit), such that solder from the wave adheres to the metallic surfaces of the vias and the pins, and fills the remaining spaces in the via cavities. The solder within the vias then cools and forms solder joints between the component pins and the circuit board vias.
In another approach called reflow soldering, preformed portions of solder (e.g., a fairly rigid disk shaped segment of solder and flux) attach to the pins which are inserted into their intended vias. When heat is applied, the portions of solder melt and draw into the cavities of the vias due to the solder""s affinity for metallic flux-cleaned surfaces. The solder then cools to form solder joints between the pins and the circuit board vias.
In yet another approach called intrusive reflow soldering, portions of solder paste (a mixture of solder and flux) are initially placed in or adjacent to cavities of vias of a circuit board (e.g., using a stencil or syringe-like device). The pins of the component are then positioned over the intended circuit board mounting location (i.e., over the circuit board vias). Typically, an oven then applies heat such that the flux volatizes and de-oxidizes the adjacent metallic surfaces. Next, the solder melts and migrates to these metallic surfaces of the pins and the vias thus filling the via cavities with solder. The solder then cools and forms solder joints between the component pins and the circuit board vias.
In some applications it would be useful to connect two circuit board sections (i.e., a small section of circuit board material or a small portion of a larger circuit board) together using pins and a soldering process. That is, it would be useful to solder one end of a pin to a first circuit board section, and the other end of the pin to a second circuit board section in order to connect the first and second circuit board sections together.
Unfortunately, there would be deficiencies to using conventional pins and soldering techniques to solder the ends of a pin to the first and second circuit board sections in order to connect the two sections together. For example, suppose that a circuit board manufacturer tries to connect the first and second circuit board sections together by positioning the pins and the first and second circuit board sections in a sandwiched manner and then applying heat to solder the pins to the sections. That is, suppose that the manufacturer positions the first circuit board section horizontally, inserts solder paste and pins into vias of the first circuit board section, and lays solder paste and the second circuit board section over the pins. Then, suppose that the manufacturer applies heat to melt the solder paste. In such a situation, it is likely some pins will insert into the vias at improper depths since a typical soldering pin is half the diameter of a via cavity and since there is nothing to prevent the pins from slipping through the vias of the circuit board sections. Accordingly, some pins may slip away from the top-positioned second circuit board section, and solder may escape from some via cavities leaving an inadequate amount of solder to form solder joints.
Furthermore, suppose that the circuit board manufacturer solders pins to the first circuit board section, and subsequently attempts to solder the pins to the second circuit board section. Unfortunately, there is still a likelihood that the solder joints between the pins and the first circuit board section will reflow during the second soldering process causing pins and solder to move out of their proper locations. The likely end result is inadequate and poorly formed solder joints.
In contrast to the above-described conventional pins and soldering approaches, the invention is directed to techniques for forming a connection between a pin and a circuit board using a pin having protruding portions and grooved surfaces that extend between the protruding portions. The protruding portions prevent the pin from inadvertently slipping through a via of the circuit board, and maintain its proper position. The grooved surfaces enable gas to vent from a cavity in the via during the solder process. Such venting prevents gas pockets or bubbles from forming within the via cavity that could form cracks or intermittent electrical connections between the pin and the via. Accordingly, such gas venting enables solder to flow within the via and form a reliable and robust solder joint between the pin and the circuit board via.
In one arrangement, the protruding portions and grooved surfaces are at both ends of the pin enabling the pin to be properly soldered between two circuit board sections. In one arrangement, the pin is simultaneously soldered to both circuit board sections. In another arrangement, the pin is initially soldered to one circuit board section, and subsequently soldered to another circuit board section. In either arrangement, the protruding portions of the pin facilitate positioning of the pin in its proper location and the additional surface area provided by the grooved surfaces and the protruding portions (i.e., wetted metallic surfaces having a high affinity for solder) retain solder in the via cavities of the circuit board sections in order to form healthy solder joints. Accordingly, the invention is suitable for use in connecting multiple circuit board sections together at opposite ends of a pin.
One arrangement of the invention is directed to a method for forming a connection between a pin and a circuit board. The method includes the step of providing a pin having an elongated portion and protruding portions that extend from the elongate portion. The elongated portion has grooved surfaces that extend along the elongated portion in a parallel manner. Additionally, each grooved surface extends between a pair of the protruding portions. The method further includes the steps of inserting the pin into a via of a circuit board, and soldering the pin to the via of the circuit board. The protruding portions enable proper positioning of the pin relative to the via of the circuit board (e.g., the protruding portions create an interference fit between the pin and the top of the via thus preventing the pin from slipping through the via or too deeply into the via).
Furthermore, the protruding portions do not prevent gas within the via cavity from escaping due. Rather, the grooved surfaces extend between pairs of protruding portions thus providing openings for gas to easily escape. Accordingly, solder can easily displace the gasses within the via cavity to form a healthy solder joint between the pin and the circuit board via. Such openings also provide ideal visual inspection points for an inspector to visually confirm adequate transfer of solder to the via cavity.
In one arrangement, the elongated portion of the pin has a circular cross-section. Here, the step of providing the pin includes the step of forming a member having a post, a first disk that radially extends from a first region of the post, and a second disk that radially extends from a second region of the post. The step of providing the pin further includes the steps of (i) cutting a first set of grooves through the first disk to a first end of the post to form a first set of the protruding portions that extend from the first region of the post, and (ii) cutting a second set of grooves through the second disk to a second end of the post to form a second set of the protruding portions that extend from the second region of the post. Accordingly, the first set of protruding portions can be used to properly position the pin relative to a first circuit board section, and the second set of protruding portions can be used to properly position the pin relative to a second circuit board section.
In one arrangement, the step of soldering includes the steps of (i) providing a solder preform around a region of the pin prior to the step of inserting the pin into the via, and (ii) applying heat to form a solder joint between the via and the pin in accordance with a reflow soldering process. That is, the solder preform around the pin melts thus contributing solder to the solder joint. As a result, the invention is suitable for use with a reflow soldering process.
In another arrangement, the step of soldering includes the steps of (i) providing a portion of solder paste to the via of the circuit board prior to the step of inserting the pin into the via (e.g., using a stencil, a syringe-like device, etc.), and (ii) applying heat to form a solder joint between the via and the pin in accordance with an intrusive reflow soldering process. Here, flux within the solder paste activates and volatizes during the soldering process, and solder from the solder paste contributes to the solder joint. Accordingly, the invention is also suitable for use with a reflow soldering process.
In one arrangement, close tolerances exist between the pin and the via. This allows the pin to be sized relatively large for improved reliability and performance, and facilitates pin registration and solder retention within the via cavity during the soldering process.
The features of the invention, as described above, may be employed in computer-related systems, devices and manufacturing procedures such as those of EMC Corporation of Hopkinton, Mass.